In applications such as the production of fibers, films, nonwovens, and molded parts from polyarylene sulfide resins, it is desirable that the viscosity and molecular weight of the polymer resin remain substantially unchanged during processing of the polymer. In addition, it is desirable for the polyarylene sulfide resin to contain a minimal amount of volatile components as it is well known that volatile components of polymer compositions can have a negative impact on polymer processing.
Various procedures have been utilized to stabilize polyarylene sulfide compositions such as polyphenylene sulfide (PPS) against changes in physical properties during polymer processing.
U.S. Pat. No. 5,235,034 discloses that poly(arylene sulfide/sulfone) polymers are treated in order to increase melt stability and decrease impurities by contacting the poly(arylene sulfide/sulfone) polymer with a soluble zinc compound and an acidic solution.
U.S. Pat. No. 5,789,533 discloses that a zinc compound is added to a polymer slurry in a polymerization system or in an aftertreatment step a pH of which slurry as determined [in the specification] is set in a range of from 12.5 to 10.5. The reference further discloses an embodiment of the invention where polyarylene sulfide is treated with a zinc compound in aftertreatment, a zinc compound (or its solution) is preferably added to a polymer slurry obtained after the polymerization, and stirred at 30° C. to 270° C. for 10 minutes to 1 hour. Then, the polyarylene sulfide is separated and purified in a conventional manner, and preferably, further treated with an acid.
WO 2009/060524 discloses a process of subjecting a polyphenylene sulfide resin to acid treatment and thermal oxidation successively to produce a polyphenylene sulfide resin having specified properties, including (1) the quantity of gas vaporizing in heat-melting the resin under vacuum at 320° C. for 2 hours is 0.3 wt % or below.
Polyarylene sulfide compositions exhibiting improved thermal and/or thermo-oxidative stability and reduced volatile content continue to be sought, as are methods to provide improved thermal and/or thermo-oxidative stability to polyarylene sulfide compositions having reduced volatile content, especially polyphenylene sulfide compositions.